1. Field of the Invention
This invention relates generally to injection molding and particularly to nozzles used to convey melt from a plasticizing unit to cavities of a mold assembly. More particularly, the present invention relates to seals for preventing pressurized melt from escaping past a nozzle fitted in a mold assembly.
2. Description of Related Art
Injection molding is a cyclic process wherein material to be molded is converted to a flowable mass (so-called “melt”), a predetermined quantity of melt is propelled into mold cavities and allowed to solidify and the resulting articles are removed from the mold cavities. Mold cavities are formed by mating mold components of mold assemblies, the mating mold components being brought into engagement for mold filling and curing, and separated for removal of molded articles. The mold assemblies are mounted in a clamp unit comprising movable members carrying the mold components and elements for producing the forces required to hold the mating mold components in mating engagement during mold filling. Raw material to be molded is converted from pellet and/or powder form to melt by an injection unit where the raw material is heated and mechanically worked. The injection unit accumulates the predetermined quantity of melt and propels the melt into the mold cavities by application of force to the melt. Melt is conveyed through conduits comprising the mold assembly to the mold cavities. Melt enters the mold cavities through one or more small openings (so-called “gates”). It is known to provide a nozzle for each gate to increase the velocity and dispersion of melt entering the mold cavities, the nozzles reducing the cross-section through which melt passes between the conduits and the gates.
It is known to provide nozzle sealing members for creating a seal between a nozzle and the member of a mold assembly receiving the outlet end of the nozzle so as to prevent pressurized melt from bypassing the nozzle and leaking from the mold assembly. Known seals are located proximate the outlet end of the nozzle and comprise extensions of the nozzle body or nozzle tip. Thermal expansion and/or deformation from forces transmitted through the melt maintain proximity and/or contact of sealing members with surfaces of the mold member to seal against leakage of melt past the sealing members. To reduce heat transfer between heated nozzles and mold members, it is known to provide gap sealing means wherein a gap established between a gap sealing surface associated with the nozzle and a gap sealing surface associated with the mold member is effective to inhibit flow of melt through the gap. In the known seal arrangements, the sealing members are either fixed to the nozzle mechanically or by press fit relying on elasticity of the sealing member to maintain adequate retention forces.